Flow velocity and direction instrument

ABSTRACT

An instrument for providing measurements of both the magnitude and direction of flow velocities in a flow field. A probe is oriented in the flow field by two servo systems which impart two angular motions to the probe to aline it with the direction of the flow. The two angular motions are indicative of the direction of flow and the magnitude of the flow velocity is then measured by conventional means.

United States Patent Maiden et a1.

FLOW VELOCITY AND DIRECTION INSTRUMENT Inventors: Donald L. Maiden,Williamsburg; James H. Monteith, Newport News; Thomas D. Carpini,Hampton, all of Va.

Assignee: The United States of America as represented by theAdministrator of the National Aeronautics and Space AdministrationFiled: July 27, 1971 Appl. No.: 166,541

US. Cl. ..73/189, 73/147, 73/182, 73/212 Int. Cl. ..G0lm 9/00 Field ofSearch ..73/147, 182, 212, 180, 189

[ 5] Oct. 24, 1972 [56] References Cited UNITED STATES PATENTS 3,329,0167/1967 heavens et a1 ..73/182 3,474,669 10/1969 Carter et a1 ..73/1 89Primary ExaminerDonald O. Woodiel Att0rney--Howard J. Osborn et a1.

[5 7] ABSTRACT An instrument for providing measurements of both themagnitude and direction of flow velocities in a flow field. A probe isoriented in the flow field by two servo systems which impart two angularmotions to the probe to aline it with the direction of the flow. The twoangular motions are indicative of the direction of flow and themagnitude of the flow velocity is then measured by conventional means.

7 Claims, '3 Drawing Figures PATENTEDnm24 me 3.699.811

SHEET 1 [IF 2 III! L 9 5 O: I'- w 0 01 5 INVENTORS DONALD L. MAIDENJAMES H. MONTEITH BY THOMAS D. RP l PATENTEDHIIT24 I912 Y 3.699.811

SHEET 2 [IF 2 43 PRESSURE TRANSDUCER METER 44 PRESSURE SERvo 47TRANSDUCER AMPLIFIER PRESSURE SERvo I R I 52) TRANSDUCE 9 T AMPLIIZIER KI I 497 54 L SYNCHRO I TRANSMITTER 25 l GEAR ANGLE INDICATDR I 48 I R I-QC TACHDMETER SERvo MOTOR I SYNCHRO I I TRANSMITTER I ANGLE I NDI ATDRGEAR : I 0C I-' TACHOMETER l v l T 5S SERvo MOTOR 27DONALDINIYEIGIZORESN ID FIG. 3 JAMES H. MONTEITH *Mmg ATTOR FLOWVELOCITY AND DIRECTION INSTRUMENT ORIGIN OF THE INVENTION The inventiondescribed herein was made by employees of the United States Governmentand may be manufactured and used by or for the Government forgovernmental purposes without the payment of any royalties thereon ortherefor.

BACKGROUND OF THE INVENTION This invention relates generally to flowvelocity measurements and more specifically concerns a device formeasuring both the magnitude and direction of flow velocities in a flowfield.

In wind tunnel research, it has become more and more necessary to studythe three-dimensional flow characteristics around the model. Themagnitude and angular orientation of the airflow are of particularinterest to the researchers. Various techniques and probe types havebeen designed to obtain this information. In small tunnels fixed probesare often used. The disadvantages of these fixed probes are that theyhave limited angular ranges and must have special calibrations which mayalways be questioned. In larger tunnels or on aircraft automatic nullseeking probes can be used. This type of probe seeks out the directionof the wind velocity vector, and then by standard pitot techniques,determines its magnitude. In the past, automatic direction seekingprobes were too large and did not provide the proper spatial resolution.Also, in many cases, they disturb the flow characteristics and they donot provide the necessary accuracy in their measurements.

It is therefore an object of this invention to provide an automatic nullseeking probe that provides accurate measurements of both the directionand magnitude of a flow field.

Another object of this invention is to provide an automatic null seekingprobe that disturbs the flow characteristics very little whileinterrogating a point in a flow field.

A further object of this invention is to provide an automatic nullseeking probe that maintains a given point in space while searching fora null.

Other objects will become apparent hereinafter in the specification anddrawings.

SUMMARY OF THE INVENTION The null seeking probe which constitutes thisinvention has five pressure ports on its hemispherical face. The axialport is connected to one side of a differential pressure transducer, andthe static ports on the body of v the probe are connected to the otherside of the transducer. This differential pressureis used to yield flowvelocity data after the probe has found a null and is alined with thedirection of flow. The other four ports consist of two sets of diagonalpairs. Each pair is connected to a differential pressure transducerwhich provides error signals for one of the two positioning servomechanisms controlling one of the two angular motions of the probe. Whenthe probe is in a nulled condition, the pressures of the ports areequal, and thus, the error signals are zero. In this condition the probeis alined with the direction of flow. The measurement of the pitotpressure yields the magnitude of the flow velocity,

and the measurements of the two angular motions of the probe areindicative of the direction of the flow velocity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic drawing showingthe mechanical components of the invention;

FIG. 2 is a schematic drawing of the hemispherical face 15 of the probein FIG. 1; and

FIG. 3 is a block diagram of an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Turning now to the embodiment ofthe invention selected for illustration in the drawings, FIG. 1 is aschematic drawing of the mechanical components of this invention. Thesensing part 11 of the probe is a tube having three linear portions 12,13 and 14. Located on the end of linear portion 12 is a hemisphericalface 15 having five pressure ports which are disclosed in FIG. 2. Alsolocated on the linear portion 12 are static pressure ports 16. An axis17 through the linear portion 12 makes an angle of 22 /2 with an axis 18through the linear portion 14. A housing 19 has three linear portions20, 21 and 22. The linear portion 20 is alined with axis 18 and thelinear portion 22 is alined with an axis 23 which makes an angle of22'/2 with axis 18. Axes 17, 18 and 23 intersect at a point on thesurface of face 15. A servo motor 24 is suitably attached to housing 19and is mechanically connected through a gear 25 to the linear portion 14of sensing part 11 to rotate sensing part 11 about axis 18. Axis 17 isthe generatrix of a 22% conical surface when revolved about axis 18. Ahousing 26 suitable for locating the hemispherical face 15 of the probeat any desired point in a flow field is alined with axis 23. A servomotor 27 is suitably attached to housing 26 and is mechanicallyconnected to the linear portion 22 of housing 19 through a gear 28 torotate housing 19 about axis 23. Axis 18 is the generatrix of a second22% conical surface when revolved about axis 23. With the condition thatthe vertex angles of the two generated cones are equal, then rotationsabout axis 18 and 23 allow the probe to assume any orientation withinthe confines of a third cone. This cone has a 45 angle. Thus, the conecan assume yaw and pitch angles up to plus or minus 45, while the centerof probe face 15 maintains a fixed point in space.

The hemispherical face 15 of the probe as shown in FIG. 2 includes aport 30 which is located on axis 17. Located on both sides of this port30 are ports 31 and 32 which are in line with port 30. Also, located inline and on both sides of port 30 are ports 33 and 34. The linecontaining ports 33 and 34 is perpendicular to the line containing ports31 and 32.

Sensing part 11 and housings l9 and 26 can be made from stainless steeltubing or any other suitable material that is available. Ports l6 and30-34 are connected to pressure transducer (not shown in FIG. 1) bymeans of tubing (not shown) from the ports through sensing part 11 andhousings 19 to 26 to the transducers. Also not shown in the drawing areelectrical connections, and ac. tachometers and synchro transmittersconnected to the shafts of servo motors 24 and 27.

Referring now to FIG. 3, a differential pressure transducer 40 isconnected to static ports 16 and axial port 30 on the hemispherical faceby means of tubes 41 and 42, respectively. The output of pressuretransducer 40 is an electrical signal, representing the differencebetween the pressures at these ports, which is measured by a meter 43.The measurement made by meter 43 is the magnitude of the flow velocity.A pressure transducer 44 is connected to ports 31 and 32 by means oftubes 45 and 46, respectively. Transducer 44 produces an electricalsignal which is proportional to the difference in the pressures at ports31 and 32. This signal is applied through a servo amplifier 47 to servomotor 24 which acting through gear changes the position of hemisphericalface 15 such that the pressure at these two ports become equal. Servomotor 24 also drives an ac. tachometer 48 to produce a damping signalthat is applied to servo amplifier 47. A synchro transmitter 49 isconnected to the shaftof servo motor 24 to produce a signal that ismeasured by an angle indicator 50 to give an indication of the positionof the shaft of servo motor 24. Ports 33 and 34 are connected to adifferential pressure transducer 51 by means of tubes 52 and 53,respectively. The difference electrical signal produced by transducer 51is applied through servo amplifier 54 to servo motor 27 which driveshousing 19 (FIG. 1') that has a servo motor 24 attached thereto. An a.c.tachometer 55 is connected to the shaft of servo motor 27 to produce adamping signal that is applied to servo amplifier 54. A synchrotransmitter 56 is also attached to the shaft of motor 27 to provide asignal that is measured by an angle indicator 57 to give an indicationof the shaft position of servo motor 27.

In the operation of the invention the hemispherical face 15 of the probeis placed at the desired point in a flow field by means of the housing26. Then the difference in pressure at ports 31 and 32 causes anelectrical error signal to be produced at the output of pressuretransducer 44. This error signal is applied to the servo motor 24 whichrotates sensing part 11 of the probe about axis 18 until the pressuresat these two ports are equal. Simultaneously, the difference ispressures at ports 33 and 34 on the hemispherical face 15 of the probecauses pressure transducer 51 to produce a second electrical errorsignal. This second error signal is applied to the servo motor 27 whichrotates housing 19 about axis 23 until the pressures at these two portsare equal. When both of the servo motors 24 and 27 have rotated to anull position, the flow in the flow field is parallel to axis 17. Thevelocity of this flow is proportional to the differential pressure atthe axial port and the static ports 16 which are connected to thetransducer 40 by tubes 41 and 42. The resulting electrical signal ismeasured by meter 43 giving an indication of the magnitude of the flowvelocity in the flow field. The readings on angle indicators 50 and 57give the direction of flow of the flow field.

The advantages of this invention are that it provides an inexpensive,accurate instrument for measuring both the magnitude and direction ofthe flow velocity in a flow field. It provides a null seeking probe thatmaintains a selected point in the flow field while searching for a nulland that disturbs the flow characteristics very little whileinterrogating the selected point.

It is to be understood that the form of the invention herewith shown anddescribed is to be taken as a preferred embodiment. Various changes maybe made in the shape, size and arrangement of parts. For example,equivalent elements may be substituted for those il-. lustrated anddescribed herein such as pressure transducer s, angle indicators, a.c.tachometers and synchro transmitters and the angles between axes l7 and18, and 18 and 23 may be any acute angle other than 22 W as long as thetwo angles are equal without departing from the spirit or scope of theinvention as defined in the following claims. 1

What is claimed is:

1. An instrument for providing the measurements of the magnitude and thedirection of a flow velocity at a fixed point comprising:

first sensing means for producing a signal indicative of the magnitudeof the flow velocity at said fixed point;

second sensing means for producing signals indicative of the magnitudeof the pressures at a first couple of point located on a first straightline with said fixed point; third sensing means for producing signalsindicative of the magnitude of the pressures at a second couple ofpoints located on a second line with said fixed point said second linebeing transverse .to said first line; I first servo means receiving thesignals indicative of the magnitude of the pressures at said firstcouple of points for repositioning said second sensing means and saidfirst couple of points such that the pressures at said first couple ofpoints are equal; I

second servo means receiving the signals indicative of the magnitude ofthe pressures at said second couple of points for repositioning saidthird sensing means and said second couple of points such that thepressures at said second couple of points are equal;

means for measuring said signal indicative of the magnitude of said flowvelocity at said fixed point after said second and third sensing meanshave been repositioned whereby said measurement is indicative of theflow velocity at said fixed point; and

means for measuring the positions of said first and second servo meanswhereby said measurements are indicative of the direction of the flowvelocity at said fixed point.

2. An instrument according to claim 1 wherein said first, second andthird sensing means includes a probe having five ports on its sensingend with a first port located at said fixed point, with a second and athird port located at said first couple of points and with a fourth anda fifth port located at said second couple of points.

3. An instrument according to claim 2 wherein said first sensing meansfurther includes static ports and means for measuring the difference inpressure between said first port and said static ports.

4. An instrument according to claim 1 wherein said first, second andthird sensing means includes a probe comprising:

a first fixed section, a second section movable with respect to saidfirst section about a first axis of said fixed point with a face havingsaid five ports.

6. An instrument according to claim 4 wherein the motor included withsaid first servo means is fixed with respect to said second section andconnected to said third section to rotate it about said second axis.

7. An instrument according to claim 6 wherein the motor included withsaid second servo means is fixed with respect to said first section andconnected to said second section to rotate it about said first axis.

1. An instrument for providing the measurements of the magnitude and thedirection of a flow velocity at a fixed point comprising: first sensingmeans for producing a signal indicative of the magnitude of the flowvelocity at said fixed point; second sensing means for producing signalsindicative of the magnitude of the pressures at a first couple of pointlocated on a first straight line with said fixed point; third sensingmeans for producing signals indicative of the magnitude of the pressuresat a second couple of points located on a second line with said fixedpoint said second line being transverse to said first line; first servomeans receiving the signals indicative of the magnitude of the pressuresat said first couple of points for repositioning said second sensingmeans and said first couple of points such that the pressures at saidfirst couple of points are equal; second servo means receiving thesignals indicative of the magnitude of the pressures at said secondcouple of points for repositioning said third sensing means and saidsecond couple of points such that the pressures at said second couple ofpoints are equal; means for measuring said signal indicative of themagnitude of said flow velocity at said fixed point after said secondand third sensing means have been repositioned whereby said measurementis indicative of the flow velocity at said fixed point; and means formeasuring the positions of said first and second servo means wherebysaid measurements are indicative of the direction of the flow velocityat said fixed point.
 2. An instrument according to claim 1 wherein saidfirst, second and third sensing means includes a probe having five portson its sensing end with a first port located at said fixed point, with asecond and a third port located at said first couple of points and witha fourth and a fifth port located at said second couple of points.
 3. Aninstrument according to claim 2 wherein said first sensing means furtherincludes static ports and means for measuring the difference in pressurebetween said first port and said static ports.
 4. An instrumentaccording to claim 1 wherein said first, second and third sensing meansincludes a probe comprising: a first fixed section, a second sectionmovable with respect to said first section about a first axis ofrotation that passes through said fixed point; and a third sectionmovable with respect to said second section about a second axis ofrotation that passes through said fixed points and makes a first acuteangle with said first axis of rotation said third section including anelongated portion along a third axis that passes through said fixedpoint and makes a second acute angle with said second axis of rotationthat is equal to said first acute angle.
 5. An instrument according toclaim 4 wherein said elongated portion of said third section isterminated at said fixed point with a face having said five ports.
 6. Aninstrument according to claim 4 wherein the motor included with saidfirst servo means is fixed with respect to said second section andconnected to said third section to rotate it about said second axis. 7.An instrument according to claim 6 wherein the motor included with saidsecond servo means is fixed with respect to said first section andconnected to said second section to rotate it about said first axis.